The present invention relates to a meltblown fibrous insulation media of thermoplastic fibers and, in particular, to a meltblown fibrous insulation media of thermoplastic fibers which is especially suited for use as an acoustical insulation and the method of making such an insulation.
Fibrous insulation media are used for many thermal and/or acoustical applications including but not limited to the acoustical insulations in appliances which reduce the sound emitted into the surrounding areas of a home, acoustical insulations used in office partitions and wall panels, and the acoustical insulations used in vehicles and aircraft which function to isolate the passenger compartment from unwanted sounds or sound levels occurring outside of the passenger compartment. Currently, there are several forms of fibrous acoustical insulation media used as acoustical insulations for such applications and especially, for vehicle passenger compartments. One form of acoustical insulation used in vehicles is cotton shoddy. While this form of acoustical insulation media is inexpensive, it does not perform particularly well when compared to other automotive insulations currently on the market. Other forms of acoustical insulation media used in vehicles include a fibrous mat with a separate cover layer (a scrim, non-woven fabric, film or foil) laminated to a major surface of the mat such as marketed by Minnesota Mining and Manufacturing Company under the trademark "THINSULATE" (also see U.S. Pat. No. 5,298,694) and such as manufactured and sold by Johns Manville International, Inc.
The process for producing the acoustical insulation media manufactured and sold by Johns Manville International, Inc., essentially includes three processes. In the first process, a thin but meltblown tightly bonded cover stock is formed having a basis weight of about 0.75 oz/yd.sup.2 or another cover stock, such as but not limited to a spun bond cover stock is formed. In the second process an air-laid, non-woven mat or fibrous layer of loose lofty randomly oriented meltblown thermoplastic fibers, e.g. fibers having a mean diameter of about 13.5 microns, and of the required thickness is formed. In a third process a heated pin or calendar roll collates a layer of cover stock onto each major surface of the mat or fibrous layer and, through the heated pins of a pin or calendar roll, heat point bonds the layers of cover stock to the major surfaces of the mat. As discussed above, the resulting product is a fibrous acoustical insulation media with a fibrous core layer of loose lofty fibers encapsulated between two surface layers of cover stock that are heat point bonded to the fibrous core layer. The loose fibers within the media provide an effective surface area for good acoustical absorption of sound waves and the films provide airflow resistance barriers for additional acoustical absorption of sound waves. The heat point bonding of the layers of cover stock to the fibrous core layer provides the acoustical insulation media with added integrity and improves the "handle-ability" of the product. While fibrous acoustical insulation media, such as this media, provide acceptable sound absorption for many applications, there has remained a need for acoustical sound absorption media with equal or better sound absorption properties, that can be more economically produced.